Conversion of alkyl aromatic hydrocarbons into alkenyl aromatic hydrocarbons



ay 4, B948. H. A. CHENEY Er AL 2,443,095

CONVERSION OF ALKYL AROMATIC HYDROCARBNS INTO ALKENYL AROMATICHYDROCRBONS Filed Aug. zo, 194e 2| Rencflon 15;.. e :rt-z

Patented May 4, 1948 CONVERSION F ALKYL AROMATIC HYDRO- CARBONS INTOALKENYL AROMATIC HY- DROCARBONS Harry A. Cheney, Berkeley, and Sumner H.Mc- Allister, Lafayette, Calii., assignors to Shell Development Company,San Francisco, Calif., a

- corporation of Delaware Application August zo, 194s, serial No.691,860

12 claim (c1. 26o-ess) The present invention relates to the producfromalkyl aromatic hydrocarbons containing at least one alkyl group of atleast three carbon atoms. 'I'he invention relates more particularly totheproduction of vinyl aromatic hydrocarbons from alkyl aromatichydrocarbons containing at least one substituent isopropyl group. Aspeciic embodiment of the invention relates to the production of styrenefrom isopropyl benzene.

'I'he olefin-substituted aromatic hydrocarbons are employed as startingor intermediate materials in a great number of important iields ofapplication. The vinyl aromatic hydrocarbons, for example, are of valueas starting materials in the production of synthetic rubber and a widevariety of chemical derivatives. The alkyl aromatic hydrocarbonsconstitute an important potential source of olefin-substitutedaromatics. Thus a straightforward dehydrogenation of an alkyl aromaticprovides the corresponding olensubstituted aromatic hydrocarbon. essesare, however, dependent upon the alkyl aromatic corresponding to thedesired olefin-substituted aromatic as charge. These processes thereforeexclude the use of alkyl aromatics often more readily available orproduced more economically than the alkyl aromatic corresponding to theolefin-substituted aromatic required. They are rendered particularlyunattractive where the alkyl aromatic corresponding to theolen-substituted aromatic is itself in greater demand than the latter.This is often the case, for example, with hydrocarbons such as ethylbenzene' and styrene. The demand for ethyl benzenes as such occasions aneed for a source of styrene other than this alkyl aromatic.

Processes have been disclosed heretofore for the production ofolefin-substituted aromatics from alkyl aromatics having a greaternumber of carbon atoms. Such processes as disclosed heretofore are,however, generally handicapped by a low yield of the olefin-substitutedhydrocarbon. They generally unavoidably involve accompanying sidereactions which often predominate, thereby not only producing anexceedingly low yield of the desired olefin-substituted aromatichydrocarbon but also converting at least i a substantial part of thecharge to less valuable by-products. Such is the case when producing,for example, styrene from isopropyl benzene by processes disclosedheretofore. The resulting reaction product generally comprises not onlyan exceedingly small proportion of styrene but also Such procy consistspredominantly of such products as alpha-methyl styrene and hydrogen, aswell as considerable amounts of benzene and propylene.

It is an object of the present invention to vprovide an improved,continuous, unitary process for the more eiilcient production ofolefin-substituted aromatic hydrocarbons of a. lesser number of carbon-atoms from alkyl aromatic hydrocarbons containing at least one alkylgroup of at least three carbon atoms wherein a greater part of the alkylaromatic hydrocarbons charged are converted to said olefin-substitutedaromatic hydrocarbon.

A further object of the invention is the provision of an improvedprocess for the more eilicient production of an olen-substitutedaromatic hydrocarbon from an aykyl aromatic hydrocarbon having at leastone alkyl group connected to the aromatic nucleus lby carbon to carbonlinkage of a secondary carbon atom in the alkyl group to a carbon atomin the aromatic nucleus.

Still another object of the invention is the provision of an improvedprocess for -the more efficient production of vinyl aromatic hydrocar-4bons from alkyl aromatic hydrocarbons having at least one isopropylgroup directly attached to a carbon atom in the aromatic ring.

A more particular object of the invention is the provision of animproved process for the more efficient production of styrene fromisopropyl benzene. Other objects and advantages of the invention willbecome apparent from the following detailed description thereof.

In accordance with the process of the invention an alkyl aromatichydrocarbon containing at least one alkyl group of at least three carbonatoms is subjected to controlled destructive dehydrogenation conditionsin a first conversionv 1 oledn group as the number of carbon atoms incorresponding alkyl groups of the alkyl aromatic product hydrogen. Theolefin-substituted aromatic hydrocarbon having a lesser number of carbonatoms to the molecule than the alkyl aromatic charge thus formed isseparated from the eiiluence of the iirst conversion zone. At least aportion of the remainder of the eiiluence of the first conversion zonecomprising the ole- 1in-substituted aromatic hydrocarbon and byproducthydrogen is subjected to hydrogenating conditions in a second conversionzone, thereby saturating the olenic side chain and reconverting theolefin-substituted aromatic hydrocarbon to the alkyl aromatichydrocarbon originally charged. At least a portion of the eiliuence fromthe secondconversion zone comprising alkyl aromatic hydrocarbon isreturned to the rst conversion zone.

A particular advantage of the invention resides in the ability toproduce more eiliciently olefinsubstituted aromatic hydrocarbons havingan oleflnic linkage between the alpha and beta carbon atoms of thesubstituent olefin group from alkyl aromatic hydrocarbons containing atleast one alkyl group directly connected by carbon-tocarbon linkage of asecondary carbon atom in the alkyl group to a nuclear carbon atom in thearomatic ring. When an alkyl aromatic hydrocarbon containing at leastone alkyl group directly connected to the aromatic nucleus by a directcarbon-to-carbon linkage of a nuclear carbon atom with a secondarycarbon atom in the alkyl group is subjected to the controlleddestructive dehydrogenation conditions in the first conversion zone,there is brought about a scission of one of the alpha to beta carbonlinkages in the substituent alkyl group with the formation of a reaction-product comprising an olen-substituted aromatic hydrocarbon containingan olefinic linkage between the remaining alpha and beta carbon atoms ofthe substituent group.

Although the process of the invention is broadly applicable to theconversion of alkyl substituted aromatic hydrocarbons toolefin-substituted aromatic hydrocarbons having a lesser number ofcarbon atoms to the molecule, it is preferred to use as charge the alkylaromatic hydrocaibon having at least three but not' more than six carbonatoms in the substituent alkyl side chain. Alkyl aromatics which may beconverted in accordance with the process of the invention comprise, forexample, isopropylbenzene, di-isopropylbenzene, n propylbenzenes,isobutylbenzene, amylbenzenes, methyl-isopropylbenzenes,methylpropylbenzene, methylisobutylbenzene, methylbutylbenzene,butyiamylbenzene, isobutyl mesityiene, isopropylisobutylbenzene,isoamylbenzene, propylmesitylene, isobutyl mesitylene,isoarnylmesitylene, tert-butylbenzene and tert-p-dibutyl, benzene.

As stated above, the invention is of particular value in the productionof olefin-substituted aromatics having an oleiinic bond between thealpha and beta carbon atoms of the substituent olenic group from alkylaromatics having a substituent alkyl group directly connected bycarbonto-carbon linkage of a secondary carbon atom of the alkyl group toa nuclear carbon atom of the aromatic nucleus. Examples of thispreferred class of materials comprise, for example, isopropylbenzene,di-isopropylbenzene, propylisopropylbenzene, methylisopropylbenzene, 2phenylbutane, 2-phenylpentane, S-phenylpentane, etc.

A particularly preferred embodiment of the invention comprises theproduction of vinyl aromatics from alkyl aromatic hydrocarbonscontaining at least one isopropyl group directly connected to thearomatic nucleus. Members of this particularly preferred group of chargematerial are, for example, isopropylbenzene, and the alkylsubstitutedisopropylbenzenes such as methylisopropylbenzenes, di-isopropylbenzene,ethylisopropylbenzene, propyl-isopropylbenzene, etc.

The alkyl aromatics employed as charge to the process ofthe inventionare obtained from any suitable source. They may be separated from thecomplex products obtained in many of the pyrogenio or catalytichydrocarbon conversion processes, or they may be a product of synthesissuch as obtained, for example, by the alkylation of an aromatichydrocarbon with a suitable oleiin. Thus isopropylbenzene is produced bythe alkylatlon of benzene with propylene under suitable alkylatingconditions and with the aid of a suitable alkylation catalyst such as,for example, sulfuric acid, aluminum chloride, phosphoric acids or thelike.

The alkyl aromatic charge in the process of the invention need notnecessarily consist of only a single alkyl aromatic hydrocarbon, but maycornprise a mixture of two or more such hydrocarbons. The charge to theprocess of the invention may furthermore comprise other hydrocarbonscapable or not of undergoing conversion underl the conditions ofexecution of the process of the invention, as well as inert gaseousmaterials such as nitrogen. normally gaseous paraillns, steam, etc.

The controlled destructive dehydrogenation of the alkyl aromatics in thefirst conversion zone is obtained by the maintenance therein of welldeiined thermal or catalytic conditions. Suitable thermal conditionscomprise a temperature in the range of from about 650 C. to about 900 C.and preferably from about 650 C. to about 850 C. The reaction zone mayoptionally contain suitable inert contact materials such as, forexample, crushed brick, quartz chips, or the like. The residence time ofreactants in the reaction zone is maintained sufiiciently short toattain fission of carbon-to-carbon linkage in the alkyl chain in theabsence of any substantial complete dealkylation. The residence time mayrange, for example, from about 0.05 second to about 5 seconds, a time ofless than one second being preferred; a higher contact time may,however, be resorted to within the scope of the invention. Atmosphericor subatrnospheric pressures may be resorted to. The use of relativelylow superatmospheric pressures ranging, for example, from pressuresslightly above atmospheric to about 100 pounds gauge are somewhatpreferred. When employing the higher ltemperatures of the abovedescribed temperature range, diluent gases or vapors such as, forexample, steam, are preferably introduced into the reaction zone.

. Catalytic conditions of controlled destructive dehydrogenation arepreferably employed in the rst conversion zone. Suitable catalystscomprise broadly the oxides or suldes of the heavy metals, such as theoxides or sulfides of the metals of the groups V, VI and VlII of theperiodic table such as, for example, the oxides and suldes of one ormore of the following: tungsten, molybdenum, chromium, vanadium, copper,iron, cobalt, nickel; solid adsorptive materials such as adsorptivealumina, activated alumina, bauxite; adsorptive siliceous materials such'as the naturally occurring or synthetically produced silica-alumihacatalysts; mixtures oi at least one of the heavy metal oxides orsulfides with an oxide of aluminum. magnesium or silicon.

Particularly suitable catalysts comprise the adsorptlve materials suchas activated alumina, bauxite, activated carbonI magnesia 'or zirconiaoptionally in combination with one or more of the following: an alkalineearth metal. alkali metal, an oxide or sulfide of an Ialkaline earthmetal or alkali metal. Preferred catalysts comprise those containing anadsorptive alumina in combination with an oxide or sulfide of calcium,lithium, strontium or cerium.

Temperatures to be maintained in the ilrst conversion zone whenresorting to the use of catalytically controlled dehydrogenation thereincomprise temperatures in the range of from about 350 C. to about 750 C.and preferably from about 400 C. to about 650 C. The contact time iscontrolled to eect substantial fission of the Ialkyl side chain in theabsence of any substantial complete dealkylation of the alkyl aromatic.Contact times of from about 0.1 to about seconds have been foundsuitable. Higher contact times may, however, be resorted to within thescope of the invention. Subatmospheric, atmospheric or superatmosphericpressures may be employed when resorting to the use of catalysts.Pressures ranging from about atmospheric to about 150 pounds are,however. somewhat preferred. Introduction of diluent gases such assteam, nitrogen and the like into the catalyst-containing zone may beresorted to. The introduction of hydrogen into the nrst conversion zoneis, however, preferably avoided since such often has been found toincrease undesired side reactions such as, for example, the removal ofthe entire side chain from the aromatic nucleus.

Under the above-defined conditions the alkyl aromatics will undergo adestructive dehydrogenation in the first conversion zone consisting ofthe scission of a carbon-to-carbon linkage in the substituent alkylchain of a portion of the alkyl aromatic charge with the formation ofolensubstituted aromatic hydrocarbons containing a lesser number ofcarbon atoms to the molecule than the lalkyl aromatic charged.concomitant with the destructive dehydrogenation reaction a substantialportion oi the charge will undergo straight dehydrogenation of the alkylside chain with the formation of hydrogen and an olensubstitutedaromatic having the same number of carbon atoms to the molecule as thealkyl aromatic charged. Under the prescribed destructive dehydrogenationconditions alkyl aromatlcs containing an alkyl chain directly connectedto the aromatic nucleus by means of a secondary carbon atom in the alkylgroup will undergo a ssion of an alpha to beta carbon linkage resultingin the unsaturation of the remaining alpha to beta carbon linkage. Thusan aryl compound of the general formula CHgX HzY

result in the obtaining of a, reaction product comprising CII-X Ar-CHand Ar-CH Y each indicate an alkyl group or hydrogen. In

6 addition to the formation oi these products of lesser carbon atoms. asubstantial part ci the charge will undergo a straight dehydrogenationof the substituent alkyl group to result in an ole; iin-substitutedaromatic hydrocarbon having the same number of carbon atoms as the alimaromatic charged and hydrogen.

Hydrogenating conditions in the second conversion zone of the processcomprise the use o! a suitable hydrogenation catalyst. Suitablehydrogenation catalysts comprises for emple those consisting`essentially oi a hydrogenating metal. such as nickel, iron, cobalt andthemetals of the platinum group. The hydrogenating metals may suitablybe employed in combination with one or more of the dimcuitly reducibiemetal oxides such as thoria, ceria, mrconia and titanic.. Temperaturesin the range of for example from about 25 C. to 175 C. and preferablyfrom about 50 C. to about 125 C. and pressures in the range of fromabout atmospheric to 500 lbs. and preierably from about 50 to 100 lbs.have been found suitable. The invention is in no wise limited by thenature of catalyst or the specliic conditions employed in the secondconversion zone. The specific conditions employed therein will generallybe dependent to some degree upon the para ticular hydrocarbon chargedand the catalyst employed. Hydrogenating conditions are, however,preferably chosen which will eect the saturation of the substituentoleiln group of the olefin aro,- matic in the absence of anysubstantialhydrogenation of the aromatic nucleus.

In order to set forth more fully the nature of the invention it will bedcribed in detail herein- Alkyl aromatic hydrocarbons comprising, for

example isopropylbenzene, taken from any out side source, is forcedthrough line i into a reaction zone. The reaction zone may comprise anysuitable type of reactor such as, for example, an elongated externallyheated coil andor a reaction chamber of enlarged cross-sectional area.In the drawing the reaction zone is depicted by a reaction chamber 2.Within reactor 2 the isopropyl benzene is subjected to thermal orcatalytic controlled destructive dehydrogenation conditions as denedabove.

Preferred destructive dehydrogenating conditions comprise, i'or example,the use or a catalyst consisting of adsorptive alumina containing analkaline earth metal or oxide thereof, such as for example activatedalumina in combination with calcium pxide. Suitable temperatures in therangeof for example from 450 C. to 750 C. are maintained in the reactor2 by suitable heating means such as for example heater t.

Suitable conversion of the isopropylbenzene is obtained by contact inreactor 2 with a catalyst comprising adsorptive alumina and a promotingamount of calcium oxide at a temperature in the range of from about .400C. to about 650 C., preierably 490 C. to 590 C., Iand a pressure of fromabout atmosphericto about pounds. The temperature is maintained inreactor 2 by means of any suitable heating means such as for example aheater S. The time of contact of reactants and catalyst is maintained inthe range of from about 0.02 to about 15seconds and preferably betweenabout 0.1` and 5 seconds.

Under these conditions demethanatlon of the isopropylbenzene will occurin reactor 2 with the formation of a reaction product comprisingstyrene. Simultaneously with the demethanation of one portion of thecharge, straight dehydrogenation of another substantial part of theisopropylbenzene charge will occur with the formation ofalpha-methylstyrene and by-product hydrogen. Although the presence ofthe catalyst increases the total amount or charge converted, it will ofnecessity increase the portion of the charge undergoing straightdehydrogenation. An outstanding advantage of the invention resides inthe fact that such increase in straight dehydrogenation of the charge isoffset as described more fully below by substantially completereconversion within the system of the products of the straightdehydrogenation to the starting material. The process of the inventiontherefore brings within the realm of practicabllity a full realizationof the advantages inherent in the use of catalysts to effeet the desireddemethanation without the disadvantages encountered In processesavailable heretofore, involving the conversion of at least a substantialproportion of the charge material to products other than styrene.

Eluence from reactor 2 comprising styrene, alpha-metlrvlstyrene, andhydrogen and some lunconverted isopropylbenzene, is passed through line5 into a product separating zone indicated in the drawing byfractionator 6. Within fractionator 6 a gaseous fraction comprisingby-product hydrogen is separated from a liquid fraction comprisingstyrene, alpha-methylstyrene and isopropylbenzene. The liquid fractionis passed from fractionator 6 through line 8 into a fractionator 9.Within fractionator 9 a vapor fraction comprising styrene is separatedand eliminated from the system as a nal product through valved line I0.A fraction comprising isopropylbenzene and alpha-methylstyrene isseparated within fractionator 9 and passed therefrom through line I2 toa fractionator I3.. Any materials higher boiling than isopropylbenzenewhich may have been formed to some degree in the system are separated asbottoms in fractionator 9 and removed therefrom through valved line I4.

Within fractionator I3 a vapor fraction comprising isopropylbenzene isseparated from a liquid fraction comprising alpha-methylstyrene. Thevapor fraction is taken overhead from fractionator I3 and passed throughline I6 into line I leading to reactor 2. The liquid fraction is takenfrom fractionator I3 and forced through line Il into a second reactionzone. The second reaction zone may constitute any suitablereaction zoneof elongated restricted and/or enlarged cross-sectional area. In thedrawing the second reaction zone is represented by reaction chamber I8.Overhead from fractionator 6 comprising the by-product hydrogen formedin reactor 2 is forced through line I9 into reactor I8. Within reactorI8 the mixture of alpha-methylstyrene and byproduct hydrogen issubjected to hydrogenating conditions effecting the hydrogenation of thealpha-methylstyrene to isopropylbenzene, Hydiogenation of thealpha-methylstyrene may be carried out under suitable hydrogenatingconditions effecting the hydrogenation of alpha-methylstyrene toisopropylbenzene. Suitable hydro- .genating conditions comprise, forexample, the` use of a catalyst comprising Raney nickel at a temperaturein the range of from about 50 C. to about 100 C. and a pressure of fromabout 50 to about 100 pounds gauge. Although catalytic hydrogenatingconditions using a Raney nickel catalyst have been set forth assuitable, it is to be stressed that the invention is in no wise limitedto the use of specific hydrogenating conditions or catalysts to effectthe desired hydrogenation within reactor I8. Other suitablehydrogenating catalysts comprise, for example, the heavy metal sulfides.Effective hydrogenating conditions employing a heavy metal sulfide-typecatalyst comprise the use of a nickel sulde-tungsten sulfide catalyst ata temperature of from about 250 C. to about 350 C. at a pressure of fromabout atmospheric to about 10 atmospheres or higher. Hydrogen producedwithin the system is preferably permitted to build up during therecycling thereof to attain a molar excess oi' hydrogen overhydrocarbons to be hydrogenated in reactor I8. Additional hydrogen froman outside source may be introduced into the system through valved line2I when needed Eiiluence from reactor I8 comprising isopropylbenzene andsome unconverted alpha-methylstyrene is passed through valved line 22into fraction-ator 23. Within fractionator 23 a gaseous fractioncomprising residual gases formed within the system is separated from aliquid fraction comprising isopropylbenzene and alpha-methylstyrene. Theliquid is passed from fractionator 23 through line 24 into fractionatorI3.

Gaseous overhead is taken from fractionator 23 through valved line 25and may be passed in part into line I9 and if desired in part into lineI. However, when the hydrogen content of the gas passing through line 25is high, recycling thereof to reactor 2 is preferably avoided since theintroduction of hydrogen into reactor 2 favors complete dealkylation ofisopropylbehzene to reaction products consisting essentially of benzeneand propylene, thereby seriously detracting from the efficiency of theprocess.

Diluent materials such as for example inert gases or steam may beintroduced into the system by means of valved line 21. Elimination ofgases from the system is accomplished by bleeding from valved line 28and/or valved line 29. If desired gaseous materials may be bled fromvalved lines 28 and/or 29 and subjected in part or entirety to apurification or separation process and a portion of the thus treated gasreturned into the system.

It is seen from the foregoing that the unitary process of the inventionprovides a method for the substantially complete conversion in a,continuous highly eicient operation of substantially all of .the alkylaromatic hydrocarbon charged to the system to a final product consistingessentially only of olefin-substituted aromatic hydrocarbon containing alesser number of carbon atoms to the molecule than the hydrocarboncharge. The process of the invention, because of its completeutilization within the system of the products of straightdehydrogenation, unavoidably encountered to a substantial degree,enables the full realization of the advantages inherent in the use ofdehydrogenation catalysts to obtain the desired controlled destructivedehydrogenation without the substantial loss of charge materialencountered in the production of olefin aromatics from alkyl aromaticsof a greater number of carbon atoms by methods available heretofore.

The following examples further illustrate the process of the invention:

'zone consisting of an externally heated unpacked tubular reactor4wherein it is subjected to a temperature of about 750 C. for aperiod of0.1 second at substantially atmospheric pressure. Eiiiuence from the rstreactor is passed through a cooler into a iirst product separating zoneconsisting of a series of fraotionators wherein a gaseous fractionconsisting essentially of hydrogen and liquid fractions consistingessentially of styrene and alpha-methylstyrene respectively areseparated from the reaction products. Th'e alphamethylstyrene andnormally gaseous fractions are passed into a second conversion zone`consisting of a reaction chamber equipped with stirring means. In thesecond reactor the alpha-methylstyrene-hydrogen mixture is subjected tocatalytic hydrogenating conditions in the temperature range of from 50C. to 100 C., and a pressure of about 70 pounds in the presence of aRaney nickel catalyst. A contact time in the range of from about 5 to 12minutes is maintained. Eiuence from the second'reaction zone is passedthrough a cooler into a fractionator wherein a normally gaseous fractionis separated from a liquid fraction consisting of isopropylbenzene andunconverted alpha-methylstyrene. The liquid fraction consisting ofisopropylbenzene and alphamethylstyrene is recycled to the first productseparating zone. Hydrogenation within the system of substantially allby-product alpha-methylstyrene to isopropylbenzene is attained. Aconver-l sion per pass of isopropylbenzene of 68% is obtained `in thefirst reactor with' a yield of 33%. styrene and 20% alpha-methylstyrene.

Example II Isopropylbenzene is subjected to catalytic demethanation in afirst reactor by contact with a. catalyst consisting of calcium-promotedactivated alumina at substantially atmospheric pressure. 'I'hetemperature in the first reactor is maintained in the range of from 550C. to 560 C. Steam is added to the ispropylbenzene charge and themixture introduced into the first reactor at a. rate of 50 mols ofispropylbenzene and 100 mols of steam per liter of catalyst per hour.Eiiiuence from the iirst reactor is 'passed through a cooler into afirst product separating zone consisting of a series of fractionatorswherein a gaseous. fraction consisting essentially of hydrogen and twoliquid fractions consisting essentially of styrene andalpha-methylstyrene, respectiveiy, are separated from the reactionproducts. The alpha-methylstyrene and normally gaseous fractions arepassed into a second con- Version zone consisting of a reaction chamberequipped with stirring means. In the second reactor thealpha-methylstyrene-hydrogen mixture is subjected to catalytichydrogenating conditions in the temperature range of from 50 C. to 100C. and a pressure of about 70 pounds in the presence of a Raney nickelcatalyst. A contact time in the range of from about 5 to 12 minutes ismaintained. Eiiluence from the second reaction zone is passed through acooler into a fractionator wherein a normally gaseous fraction isseparated from a liquid fraction consisting of isopropylbenzene andunconverted alphamethylstyrene. The liquid fraction consisting ofisopropyl-benzene and alpha-methylstyrene is v recycled to the rstproduct separating zone.

Hydrogenation within the system of substantially al1 by-produetalpha-methylstyrene to isopropylbenzeney is attained. A conversion perpass of isopropylbenzene of 19.5% is obtained in the first reactor witha yield of 32% styrene and 16% alpha-methylstyrene.

Example I-II In a repetition of the process of Example II undersubstantially identical conditions but with the exception that acatalyst consisting of adsorptive alumina is employed in the firstreactor at a temperature of 650 C., a conversion per pass of ethylisopropylbenzene of 58% is obtained in the first conversion zone with ayield of 11% styrene and 62% alpha-methylstyrene.

Example IV In al repetition of the process of Example II undersubstantially identical conditions but with theuse of anothercalcium-promoted adsorptive alumina catalyst at a temperature of 650 C.in the iirst reactor aconversion per pass of isopropylbenzene of 49% isobtained in the first conversion zone with a yield of 12% styrene and65% alpha-methylstyrene.

In the yforegoing examples, because of the continuous reconversion ofthe by-product hydrogen and alpha-methylstyrene to isopropylbenzene andthe .reintroduction of the latter into the controlled destructivedehydrogenation zone, an

Cymene is subjected to catalytic demethanation in a first reactor bycontact with a catalyst consisting of calcium-promoted activated aluminaat substantially atmospheric pressure at a temperature of about '730 C.1.5 mols of steam per mol of cymene charge is employed and. the mixturepassed through the irst reactor at the rate of 2.5 mols of thecymene-steam mixture per liter of catalyst per hour. Efiluence from therst reactor is passed through a cooler into a iirst product separatingzone consisting of a series of fractionators wherein a gaseous fractionconsisting essentially of hydrogen and two liquid fractions consistingessentially of p-methylstyrene and asym. methyl p-tolylethylene,respec-' tively, are separated from the reaction products. The asym.methyl p-tolylethylene and normally gaseous fractions are introducedinto a second conversion zone wherein they are contacted with anickel-tungsten-sulde catalyst at a pressure of 4.5 atmospheres and atemperature of about 300 C. at a liquid hourly space velocity of 2.Eiiiuence from the second reaction zone is passed through a cooler intoa fractionator wherein a normally gaseous fraction is separated from aliquid fraction comprising cymene and unconverted asym. methylp-tolylethylene. The liquid fraction consisting of cymene and asym.'methyl p-tolylethylene is recycled to the first product separating zone.Hydrogenation of substantially all lay-product asym. methylp-tolylethylene to cymene is attained within the system. A conversionper pass of cymene of 60% is obtained in the first conversion zone. Theinvention claimed is:

1. A process for the production of styrene s 11 which comprisessubjecting isopropylbenzene to destructive dehydrogenating conditions ina. rst conversion zone, thereby eilecting the conversion ofisopropylbenzene to a reaction product comprising styrene,alpha-methylstyrene and hydrogen in said iirst conversion zone,separating styrene from the eiiluence of said rst conversion zone,subjecting the remaining eiiiuence of said first conversion zone tohydrogenating conditions in a second conversion zone, thereby effectingthe hydrogenation of alpha-methylstyrene Vto isopropylbenzene in saidsecond` conversion zone.' and passing eiiiuence from said secondconversion zone to said first conversion zone.

2. A process for the production of styrene which comprises subjectingisopropylbenzene to destructive dehydrogenating conditions at atemperature of from about 350 C. to about 750 C.in the presence of adehydrogenation catalyst in a first conversion zone, thereby effectingthe conversion of isopropylbenzene to a reaction product comprisingstyrene, alpha-methyistyrene and hydrogen in said first conversion zone,separating hydrocarbons comprising styrene from the eiiluence of saidrst conversion zone, subjecting at least a part of the remainingeilluence of said first conversion zone to hydrogenating conditions in asecond conversion zone, thereby effecting the hydrogenation ofaJpha-methylstyrene to isopropylbenzene in said second conversion zone,and passing at least a part of the eiiiuence from said second conversionzone to said rst conversion zone.

3. A process for the production of styrene which comprises subjectingisopropylbenzene to destructive dehydrogenating conditions at atemperature of from about A400 C. to about 650 C. in the presence of adehydrogenation catalyst in a rst conversion zone, thereby effecting theconversion of isopropylbenzene to a reaction product comprising styrene,alpha-methylstyrene and hydrogen in said rst conversion zone, separatinga, fraction comprising styrene from the eiiluence of said rst conversionzone, subjecting the remaining eiiiuence of said rst conversion zone tohydrogenating conditions in a second conversion zone, thereby effectingthe hydrogenation of alphamethylstyrene to isopropylbenzene in saidsecond conversion zone, and passing eiiiuence from said secondconversion zone to said first conversion zone.

4. A process for the production'of styrene which comprises subjectinghydrocarbons comprising isopropylbenzene to destructive dehydrogenatingconditions at a temperature of from about 400 C. to about 650 C. in thepresence of a dehydrogenation catalyst comprising adsorptive alumina ina first conversion zone, thereby effecting the conversion ofisopropylbenzene to a reaction product comprising styrene,alpha-methylstyrene and hydrogen in said first conversion zone,separating a fraction comprising styrene from the emuence of said firstconversion zone, subjecting the remaining eiiiuence of said rstconversion zone to hydrogenating conditions in a second conversion zone,thereby effecting the hydrogenation of alpha-methylstyrene toisopropylbenzene in said second conversion zone, and passing eiliuencefrom said second conversion zone to said first conversion zone.

5. A process for the production of styrene which comprises subjectingisopropylbenzene to thermal destructive dehydrogenating conditions at atemperature of from about 650 C. to about 900 C. and a residence'time offrom about'0.05 to about seconds in a iirst conversion 20m2, thi???- byeecting the conversion of isopropylbenzene to a reaction productcomprising styrene, alpha-- methylstyrene and hydrogen in said firstconversion zone, separating styrene from the eluence of said conversionzone, subjecting at least a part of the remaining effiuence of said rstconversion zone to hydrogenating conditions in a second conversion zone.thereby effecting the hydrogenation of alpha-methylstyrene toisopropylbenzene in said second conversion zone, and passing eiliuencefrom said second conversion zone to said first conversion zone.

6. A process tor the production of vinyl-substituted aromatichydrocarbons which comprises subjecting alkyl aromatics having at leastone substituent isopropyl group directly attached to the aromaticnucleus to destructive dehydrogenating conditions in la iirst conversionzone, thereby effecting the conversion of said alkyl aromatics to areaction product comprising vinyl aromatics, olefin-substitutedaromatics having the same number of carbon atoms as said alkyl aromaticcharge and hydrogen in said first conversion zone, separating vinylaromatics from the eiliuence of said iirst conversion zone, subjectingthe remaining efiiuence of said rst conversion zone to hydrogenatingconditions in a second conversion zone, thereby eiecting thehydrogenation of oleiin-substituted aromatics to alkyl aromatics in saidsecond conversion zone, and passing eluence from said second conversionzone to said first conversion zone.

7. A process for the production of vinyl-substituted aromatichydrocarbons from alkyl aromatic hydrocarbons having at least onesubstituent isopropyl group directly attached to the aromatic nucleuswhich comprises subjecting alkyl aromatics having at least onesubstituent isopropyl group directly attached to the aromatic nucleus todestructive dehydrogenating conditions at a temperature inthe range offrom about 350 C. to about 750 C. in the presence of a dehydrogenationcatalyst in a rst conversion zone, thereby effecting the conversion ofsaid alkyl aromatics to a reaction product comprising olefin-substitutedaromatics having the same number of carbon atoms as the alkyl aromaticcharge, vinylsubstituted aromatics and hydrogen in said rst conversionzone, separating vinyl-substituted aromatic hydrocarbons from theeiliuence of the rst conversion zone, subjecting the remainder of saidefiluence of the iirst conversion zone to hydrogenating conditions in asecond conversion zone, thereby eiecting the conversion ofolefin-substituted aromatics to alkyl aromatics in said secondconversion zone, and passing at least a part of the eiliuence of saidsecond conversion zone to said iirst conversion zone.

8. A process for the production of olefin-substituted aromatichydrocarbons containing a lesser number of carbon atoms from alkylaromatic hydrocarbons containing a greater number of carbon atoms whichcomprises subjecting alkyl aromatic hydrocarbons having a substituentalkyl group of at least three carbon atoms connected by a secondarycarbon atom in the alkyl group to a carbon atom in the aromatic nucleusto destructive dehydrogenating conditions in a and hydrogen in saidfirst conversion zone, separating olen-substituted aromatic hydrocarbonshaving a lesser number of carbon atoms than said alkyl aromatic chargefrom the efiluence ofsaid rst conversion zone, subjecting at least apart of the remaining eiiluence of said first conversion zone tohydrogenating conditions in a second conversion zone, thereby effectingthe hydrogenation of olefin-substituted aromatic hydrocarbons to alkylaromatic hydrocarbons in said second conversion zone and passing emuencefrom said second conversion zone to said iirst conversion zone.

9. A process for the production of olefin-substituted aromatichydrocarbons having a lesser number of carbon atoms to the molecule fromalkyl aromatic hydrocarbons having a greater number of carbon atoms tothe molecule which' comprises subjecting alkyl aromatics having at leastone substituent alkyl group of at least three carbon atoms connected bya secondary 'carbon atom in the alkyl group to a carbon -atom in thearomatic nucleus to destructive dehydrogenating conditions at atemperature in the range of irom about 350 to about 750 C. in thepresence of a dehydrogenation catalyst in a ilrst conversion zone,thereby effecting the conversion of alkyl aromatics to a reactionproduct comprising olefinsubstituted aromatics having the same number ofcarbon atoms as the alkyl aromatic charge, olefin-substituted aromaticshaving a lesser number oi carbon atoms than the alkyl -aromatic chargeand hydrogen in said ilrst conversion zone, separatingolefin-substituted aromatic hydrocarbons having a lesser number ofcarbon atoms than the aromatic charge from the eiliuence of the rstconversion zone, subjecting the remainder of said eilluence of the firstconversion zone to hydrogenating conditions in a second conversion zone,thereby effecting the conversion of olensubstituted aromatics to alkylaromatics in said second conversion zone, and passing at least a part ofthe eilluence of said second conversion zone to said ilrst conversionzone.

10. A process for the production of olefin-substituted aromatichydrocarbons yhaving a lesser number of carbon atoms to the moleculefrom alkyl aromatic hydrocarbons having a greater number of carbon atomsto the molecule which least one substituted alkyl group of at leastthree carbon atoms to destructive dehydrogenating conditions in a firstconversion zone, thereby eilecting the conversion of alkyl aromatics toa reaction product comprising olefin-substituted aro,- matics having thesame number of carbon atoms as the alkyl aromatic charge,oleiln-substituted aromatics having a lesser number of carbon atoms thanthe alkyl aromatic charge and hydrogen in said first conversion zone,separating olefin-substituted aromatic hydrocarbons having a lessernumber of carbon atoms than the aromatic charge from the eilluence ofthe first conversion zone, subjecting the remainder of said eiiluence ofthe nrst conversion zone to hydrogenatlng conditions in a secondconversion zone, thereby ei'- iecting the conversion ofolefin-substituted aromatics to alkyl aromatics in said second couver,-sio'n zone, and passing at least a part or the emuence of said secondconversion zone to said first conversion zone.

stituted aromatic hydrocarbons having a lesser number of carbon atoms tothe molecule from alkyl aromatic hydrocarbons having a greater number ofcarbon atoms to the molecule which comprises subjecting alkyl aromaticshaving at least one substituent alkyl group of atleast three carbonatoms to thermal destructive dehydrogenating conditions at a temperaturein the range of from about 650 C. to about 900 C, and a residence timeof from about 0.05 to about 5 seconds in a first conversion zone,thereby effecting the conversion of alkyl aromatics to a reactionproduct comprising. olefin-substituted aromatics having the same numberof carbon atoms as the alkyl aromatic charge, oleiln-substitutedaromatics having a lesser number of carbon atoms than the alkyl aromaticcharge and hydrogen in said ilrst conversion zone, separatingoleiln-substituted aromatic hydrocarbons having -a lesser number ofcarbon atoms than the aromatic charge from the eilluence of the ilrstconversion' zone, subjecting the remainder of said eilluence oi theiirst conversion zone to hydrogenating conditions in 4a secondconversion zone, thereby effecting th'e conversion of olefin-substitutedaromatics to alkyl aromatics in said second conversion zone, andpassing. at least a part oi' the eilluence of said second conversionzone to said rst conversion zone.

12. A process for the production of olen-substituted aromatichydrocarbons having a lesser number of carbon atoms to the molecule fromalkyl aromatic hydrocarbons having a greater number of carbon atoms tothe molecule which comprises subjecting alkyl aromatics having at leastone substituent alkyl group of at least three carbon atoms todestructive dehydrogenating conditions at a temperature in the range offrom about 350 C. to about 750 C. in the presence o! a dehydrogenationcatalyst in a first conversion zone, thereby effecting the conversion ofalkyl aromatics to a reaction product comprising oleilnsubstitutedaromatics having th'e same number of carbon atoms as'the alkyl aromaticcharge, olefin-substituted aromatics having a lesser number of carbonatoms than the alkyl aromatic charge and hydrogen in said firstconversion zone, separating olefin-substituted aromatic hydrocarbonshaving a lesser number of carbon atoms than the aromatic charge from theeilluence of the first conversion zone,l subjecting the remainder ofsaid eilluence of the rst conversion zone to hydrogenating conditions ina second conversion zone, thereby effecting the conversion oi'oleiln-substituted -aromatics to alkyl aromatics in said 4secondconversion zone, and passing at least a part of the eiliuence of saidsecond conversion zone to said rst conversion zone.

HARRY A. CHENEY. SUMNER H. MCALLIS'I'ER.

REFERENCES CITED The following references are oi record in the ille ofthis patent:

UNITED STATES PATENTS Number Name Date 2,182,313 'Dreisbach Dec. 5, 19392,182,431 Groll et al Dec. 5, 1939 2,198,185

1l. A process for the production oi oleiinsub- Stanley et al. Apr. '23,1940

